How much to save each month to reach a goal
A trip, an emergency fund, a down payment: see how to turn a goal into a monthly amount — and how interest helps.
Every savings goal fits into three numbers: how much you want to put aside, how long you have and how much your money will earn along the way. With them, you can work out what needs to come out of your pocket every month.
First, without interest
The simplest calculation is dividing the goal by the number of months. To save R$ 30,000 in 3 years (36 months), you'd need about R$ 833 a month. It's a good starting point, but it ignores an important ally: returns.
Now, with compound interest
If your savings earn interest, each deposit works for you until the goal date. Early deposits earn for longer; late ones, for less. At 10% a year (about 0.8% a month), the same R$ 30,000 goal over 36 months takes roughly R$ 723 a month. Of the total, about R$ 26,000 comes out of your pocket and around R$ 4,000 comes from interest.
Time matters more than it seems
Stretching the timeline changes the math a lot. At the same rate, saving R$ 30,000 over 5 years takes about R$ 392 a month — and the share that comes from interest rises to around R$ 6,500. Starting earlier is usually more efficient than trying to catch up later with bigger deposits.
Having some money already saved helps too: with R$ 5,000 to start, the 3-year goal drops to about R$ 562 a month.
Run your own numbers
Use the calculator below: enter what you already have, a test monthly contribution, the rate and the period. Adjust the contribution until the final amount reaches your goal.
Compound interest calculator
Final balance
R$125,302.74
- Total invested
- R$61,000.00
- R$1,000.00 upfront + 120 contributions of R$500.00
- Total interest
- R$64,302.74
- 51.32% of final balance
Equivalent monthly rate: 1.08%
Anyone who opens the link sees this same simulation. Nothing is stored.
Show year-by-year table
| Year | Total invested | Total interest | Final balance |
|---|---|---|---|
| 1 | 7,000 | 507 | 7,507 |
| 2 | 13,000 | 1,908 | 14,908 |
| 3 | 19,000 | 4,328 | 23,328 |
| 4 | 25,000 | 7,904 | 32,904 |
| 5 | 31,000 | 12,798 | 43,798 |
| 6 | 37,000 | 19,190 | 56,190 |
| 7 | 43,000 | 27,285 | 70,285 |
| 8 | 49,000 | 37,319 | 86,319 |
| 9 | 55,000 | 49,557 | 104,557 |
| 10 | 61,000 | 64,303 | 125,303 |
Contributions at the end of each month (the first one at the end of month 1). Yearly rate converted to the equivalent monthly rate. Taxes, fees and inflation are not considered: to compare investments after tax, use the fixed income calculator.
The formula, for those who like it
With deposits at the end of each month, the required contribution is:
A = (G − P·(1+i)ⁿ) · i / [(1+i)ⁿ − 1]
Where G is the goal, P what you already have, i the monthly rate and n the number of months. A yearly rate becomes monthly through the equivalent rate: i = (1 + yearly rate)^(1/12) − 1.
Three tweaks for a realistic plan
- Inflation: if your goal is "today's price" of a trip or a car, use a real rate — the return above inflation. Alternatively, adjust the goal for expected inflation.
- Taxes and fees: income tax and management fees reduce your net return. Simulate with a slightly lower rate to leave some slack.
- Timeline and liquidity: for short-term goals or an emergency fund, prefer low-risk investments you can withdraw easily, even if they earn less.
Turn the goal into a habit
Once you know the amount, automate it: schedule a transfer for payday. Review the goal every few months — if your income goes up, raise the contribution; if money gets tight, extend the timeline instead of giving up.
Examples are illustrative and do not constitute investment advice. Past returns do not guarantee future returns.